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Re: [Discuss-gnuradio] Transmit filtering

From: Marcus D. Leech
Subject: Re: [Discuss-gnuradio] Transmit filtering
Date: Mon, 05 Sep 2011 11:46:28 -0400
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On 05/09/11 10:19 AM, John Ackermann N8UR wrote:
> I'm generating two NBFM signals, offsetting them plus and minus 25 kHz
> with FreqXlatingFilters, and combining the output in an adder which
> then drives a USRP sink.  It seems sensible to put a bandpass filter
> on the result.
> I have a basic conceptual confusion.  I would think that you'd specify
> a bandpass filter around zero with a low cutoff of, say, -40e3 and a
> high cutoff of +40e3.  However, this doesn't work -- the bandpass
> filter seems to require a number >0 for the lowpass frequency.
Make sure that you specify complex-taps.  I assume you're using GRC.  By
default, it uses the version of
  the bandpass filter with real taps.  But if you specify complex taps,
you can use negative frequencies.

Principal Investigator
Shirleys Bay Radio Astronomy Consortium

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